Ester based lubricant composition containing phenothiazine and aminopyridine



7 3,038,858 ESTER BASED LUBRICANT COMPOSITION CON- TAIlEING PHENOTHIAZINE AND AMINOPYRI- DIN Guy M. Verley, Harvey, Ill., assignor to Sinclair Refining Company, New York, N.Y., a corporation of Maine No Drawing. Filed June 16, 1959, Ser. No. 820,600 10 Claims. (Cl. 252-47) This invention relates to ester-based lubricant compositions and more particularly to ester-based lubricant compositions containing phenothiazine and aminopyridine which are effective as corrosion inhibitors or antioxidants.

Organic compounds, such as lubricating oils, undergo oxidation upon exposure to air. This process is accentuated by elevated temperatures such as occur in engines and other operating machinery. When such organic compositions are used as motor or machinery lubricants, their stability is still further drastically reduced due to their contact with metal surfaces which give up metallic particles into the lubricant. Such abraded or dissolved metals or metal salts appear to act as oxidation catalysts in the lubricant causing the formation of primary oxidation products which in turn cause further degradation of the organic compounds present in the composition. In addition, water also causes corrosion of metallic surfaces and accentuates oxidation of the lubricant. Problems of this nature are encountered in mineral oils but appear to be particularly troublesome in synthetic oleaginous fluids exemplified by esters. Numerous oxidation and corrosion inhibitors have been found for use in lubricating compositions and many combinations thereof also have been tested. In many instances the effect of such combination is merely the effect of each of the inhibitors employed, but in other cases a greater effect is exhibited by the additives used, thus promoting to an unaccountable degree the oxidation and corrosion protection of the composition.

7 It is the particular object of the invention to provide an ester oil of lubricating viscosity having the superior lubricant properties characteristic of the synthetic ester oils, and inhibited With respect to oxidation deterioration. Further, the additives of this invention have proven to be effective in retarding sludge formation in synthetic ester lubricants which are exposed to high temperatures, and also have proven far more effective than the conventional use of phenothiazine alone in retarding sludge formation in ester fluids made from a branched neostructured alcohol component.

The present invention provides an improved ester-based lubricant composition containing phenothiazine and aminopyridine so as to exhibit increased resistance to oxidation under high temperatures such as in excess of 400 F.

The preferred amines utilized in this invention are 2-aminopyridine, 2,6-diaminopyridine, 4-methyl-2-aminopyridine and their substituted derivatives. The aminopyridine may be added in amounts from about .01 to 5 percent by weight of final composition with a preferred amount of from about .1 to 2 percent by weight of final composition. The additive selected from this group is normally added to the ester-based lubricant along with the phenothiazine. The phenothiazine is normally present in amounts from about .01 to 5 percent by weight of final composition with a preferred amount being from about .1 to 2 percent, and the phenothiazine maybe substitu-ted as with alkyl groups. The relative concentrations of the additives will vary with the particular ester lubricant employed and also dependent upon the characteristics of the final lubricant composition desired. Normally, it is preferred that the amine to phenothiazine ratio should be greater than about 1 to 1.

The lubricant composition of this invention includes as the mayor component a base oil which is an ester of lubricating viscosity which may be, for instance, a simple ester or compounds having multiple ester grouping such as in complex esters, polyesters or diesters. These esters; are made from monoand polyfunctional aliphatic alcohols and aliphatic carboxylic acids, frequently of about. 4 to 12 carbon atoms. The reaction product of a monofunctional alcohol and a monocarboxylic acid is usually considered to be a simple ester. A diester is usually considered to be the reaction product of 1 mole of a dicarboxylic acid say of 6 to 10 carbon atoms with 2 moles of a monohydric alcohol of, for instance 6 to 12 carbon atoms or of 1 mole of a glycol of 4 to 10 carbon atoms with two moles of a monocarboxylic acid of 4 to '10 carbon atoms. The diesters frequently contain from 20 to 40 carbon atoms. A complex ester is usually considered to be of the type XY-ZYX in which X represents a monoalcohol residue, Y represents a dicarboxylic acid residue and Z represents a glycol residue and the linkages are ester linkages. Those esters, wherein X represents a monoacid residue, Y represents a glycol residue and Z represents a dibasic acid residue are also considered to be complex esters. The complex esters often have 30 to 50 carbon atoms. Polyesters, or poly: ester bright stocks can be prepared by direct esterification of dibasic acids with glycols in about equimolar quantities. The polyesterification reaction is usually continued until the product has a kinematic viscosity from about 15 to 200 centis-tokes at 210 F., and preferably 40 to centistokes at 210 F.

Although each of these products in itself is useful as a lubricant, they are particularly useful when added or blended with each other in synthetic lubricant compositions. These esters and blends have been found to-be especially adaptable to the conditions to which turbine engines are exposed, since they can be formulated to give a desirable combination of high flash point, low pour point, and high viscosity at elevated temperatures, and need contain no additives which might leave a residue upon volatilization. In addition, many complex esters have shown good stability to shear. Natural esters, such as castor oil may also be included in the blends, as may be up to about 1 percent or more by weight of a foam inhibitor such as a methyl silicone polymer or other additives to provide a particular characteristic, for instance, extreme pressure or load carrying agents, corrosion inhibitors, etc., can be added.

Typical synthetic lubricants may be formulated essentially from a major amount (about 60-85%) of a complex ester and a minor amount (about 15-40%) of a diester, by stirring together a quantity of diester and complex ester at an elevated temperature, altering the proportions of each component until the desired viscosity is reached. Polyesters can be employed to thicken diester base stocks to increase the load carrying capacity of the base diester oil. The polyester will generally not comprise more than about 50 weight percent of the blend, preferably about 20 to 35 weight percent. Usually the amount of the polyester employed in any blend would be at least about 5 percent, and the majority of the lubricant is a diester. Advantageously the final lubricating oil compositoin would have a maximum viscosity at 40 F. of about 13,000 centistokes and a minimum viscosity of about 7.5 centistokes at 210 F.

The monohydric alcohols employed in these esters usually contain less than about 20 carbon atoms and are generally aliphatic. Preferably the alcohol contains up to about 12 carbon atoms. Useful aliphatic alcohols include butyl, hexyl, methyl, iso-octyl, and dodecyl alcohols, C oxo alcohols and octadecyl alcohols. C to C branched chain primary alcohols are frequently used aosasas I aresuitable alcohols for use to produce the desired lubricant. If the alcoholhas no hydroge'ns' on the beta car- 1 1, bon 1atorns,uit is. moo-structured. 1 In particular, the nee-C ,alcohol 2,2,4-trimethybpentanoblfigives com- 1 1 ethyl stearate, :di-(2-ethylhexyl) :sebacate, ethylene gly- 1 1 col di-lanrate, 'di-(Zcthylhexyl) phthalat'e, di-(LB -methyI- 1 1 1 butyl) adipate, di(2-,ethylbutyl)adipate, di( l ethylpropyl) 1 1 1 adipate, 1 diethyl oxylate, glycerol tri-n-octoate, di-cyclo- 1 1 1 hexyl adipa'te', di-(undecyl) sebacate, tetraethylene glycol- 1 1 1 'di-,(2 cthylenehexoate), di-Cellosolve phthalate, 1 butyl phthallyl butyl. glycolate, di-n hexyl fumarate. polymer; 1

1 .plex'este'rs suitable for blending with. diesters to produce 1 lubricants which meet stringent viscosity requirements.

1 lso-octanol'and iso-decanol are alcohol mixtures madeby 1 :the oxoprocess'from c 43 copolymer heptenes. The

. cutwhichmakcs upiso-octanol usually contains about;

' 17% 1 3i,4-dimethylhexanol; 29% 3,5:-dimethylhexanol;v

1 1 4,5-dirnethylhexanol; 1.4% .'51,5-dimethylhexanol;

. c ols may be used, for instance, where thealkylene radi 1 cal contains 2 to 4" carbon atoms such, as'diethyIenegIy- 1 ;col, dipropylene glycol and ether glycols up to 1000 to 2000 molecular weight; The most popular glycols: for

1 the manufacture, of ester lubricants appear to-be polyn01; 2.3% 4ethylhexanol;

16% of a mixture-of B-methylheptanoland 5-ethylhepta-. 4,32% walkyl alkanols and 5% 1 1 other materials.

1 carbon atoms; however, if desired they could: contain a greater number. Among the specific glycols which can 1 be, employed are 2-ethyLL3-hexsnediol, 2-pro1pyl-3,3- 1 'heptanediol, 1 2-methyl-1,'3pentanediol, 1 2-butyl.l,3--bu-' tanediol, ZA-diphenyl-1,3 butanediol,. and 2,4-dimesityl-' 1 ;l,.3-.but anediol. 1 In addition to. these glycols; ether glyproylene glycols havingamolecular weight :ofabout 100 -3001and Z-ethyl. hexanediol. The 2,2-dimcthyl gly-i of other glycols or other materials can be present as long as the desired properties of the product are not unduly deleteriously affected. Aside from glycols, the esters may be made from polyhydric alcohols of more than two hydroxyl groups, e.g. pentaerythritol, trimethylol propane and the like.

Preferred monocarboxylic acids are those of 8 to 24 carbon atoms such as stearic, lauric, etc. The dicarboxylic acids employed in making ester lubricants will in general contain from about 4 to 12 carbon atoms. Suitable acids are described in US. 2,575,195 and include the aliphatic dibasic acids of branched or straight chain structures which are saturated or unsaturated. The preferred acids are the saturated aliphatic dicarboxylic acids containing not more than about 12 carbon atoms, and mixtures of these acids. Such acids include succinic, adipic, suberic, azelaic, and sebacic and isosebacic acid which is a mixture of oz-ethyl suberic acid, a,a'-diethyl adipic acid and sebacic acid. This composite of acids is attractive from the viewpoint of economy and availability since it is made from petroleum hydrocarbons rather than the natural oils and fats which are used in the manufacture of many other dicarboxylic acids, which natural oils and fats are frequently in short supply. The preferred dibasic acids are sebacic and azelaic or mixtures thereof. Minor amounts of adipic used with a major amount of sebacic may also be used with advantage.

Various useful ester base oils are disclosed in United States Patents Nos. 2,499,983; 2,499,984; 2,575,195; 2,575,196; 2,703,811; 2,705,724 and 2,723,286. Generally the synthetic base oils consist essentially of carbon, hydrogen and oxygen, i.e. the essential nuclear chemical structure is formed by these elements alone. However, these oils may be substituted with other elements such as halogens, e.g. chlorine and fluorine. Some representative components of ester lubricants are ethyl palmitate,

- F. to 'ZSOSUSat 2 1 'dibenzyl sebacate, and diethylene glycol 'bis(2-n-butoxy ethylcarbonate). '2-ethylhexyl-adipate-neopentyl glycyl adipate-2ethylhexy1, is a representative complex ester. 1

- Generally, thesesynthetio ester lubricants'have a viscosity. ranging from light. to heavy'oils, eg. about SOSUS at 1 1 10F and preferablySO to '150- 1 1 1 1 The estersare manufactured'in general, by mere re- 1 1 1 action of the alcoholic and acidic constituents, although 1 1 simple esters may be converted: to longer chain compo 1 treats by transesterification.' The constituents, in the pro- 1 I portions suitable for giving the desired ester, arereactfed 1 1 1 preferably in the presence of a catalystand solvent or waterentraining agent to insure maintenanceof the liquid. 1 state during-thcreaction. 1 Aromatic hydrocarbons such 1 1 as xylene ortoluene have proven satisfactory as solvents. 1

nGenerally, the glycols 1contain from about 4to' .12 1 1 The choiceof solventinfluences the choice of tempera.-

ture at whichthe esterification is conducted; for instance; 1 1

. may-be used. To provide a better reaction rate an acid 1 esterification' catalyst is often used; 1 'Many of these 1 1 catalysts are known and include,'for instance, H01, 1 1

1 H 30 NaHSO aliphatic and aromatic sulfonic acids; 1 1 1 1 phosphoric acid, hydrobromic acid, HF and dihydroxy-= 1 1 1 fluoboricaeid. Gther catalysts are thionyl chloride, boron 1 trifluoride, and silicon tetrafluoride. Titanium esters also whentoluene is used; a temperature of C isrecom 1 1 mended; with xylene, temperatures up to about 195" C;

make, 1 valuable iesterification and: transesterification 1 Qqcatalysts. Ina. preferred reaction, aboutllfito about 1 weight 200 C. While refluxing water. reaction must be suflicient to remove the water from the esterification mass as it is formed. This temperature is usually at least about 140 C. but not so high as to decompose the wanted product. The highest temperature nceded for the reaction will probably be about 200 C., preferably not over about 175 C. The pressure is conveniently about atmospheric. Although reduced pressure or superatrnospheric pressure could be utilized, there is usually no necessity to use reduced pressures, as the temperatures required at atmospheric pressure to remove the water formed do not usually unduly degrade the product.

When reacting glycols with dibasic acids to produce a polyester, it is preferred to continue the reaction with concomitant boiling off of water from the reaction mixture until the polyester product has a kinematic viscosity of about 15 to 200 centistokes at 210 F., preferably about 40 to 130 centistokes. When this point has been reached, the polymerization can be stopped, for instance, by adding a capping alcohol to the reaction mixture, and continuing to reflux until water ceases to be evolved. The capping alcohol is a low molecular weight monoalcohol of up to about 20 carbon atoms. It is standard practice, when esters are made using the conventional acid catalysts such as sodium bisulfate or paratoluenesulfonic acid to give the esters an after-treat by washing the ester with a 5 percent aqueous K CO solution or by heating the ester in an autoclave for 15 hours at 340 to 350 F. with 10 Weight percent of propylene oxide. It is also conventional to subject the ester to filtration to remove insoluble materials. After this the product may be subjected to a reduced pressure distillation or stripping at 100 to 200 C. to remove volatile materials, such as water, the solvent, and light ends.

Samples of ester fluids without an oxidation inhibitor 1 ccls', such' as ,neop'entyl glycol, havebe'en' shown to inz- -p r e bq 'a g Y,- to:015%bf1the1catah'st part heat stability to-the final blends. :Minor amounts 1 'ls'used with a xylene-solventat a temperature of to 1 I 1 The temperatures of the and samples containingaminopyridine alone, phenothiazine alone and samples made according to the present invention containing varying portions of aminopyridine and plienothiazine are compared in a modified MIL-L-9236 corrosion-oxidation tests run at 450 F. for a period of about 20 hours. The test was conducted by passing a stream of air at the rate of 5 liters per hour through 100 ml. of the sample and one inch square coupons of copper, steel and magnesium. Oil insolubles were determined -by centrifugingthe fluid upon completion of the test. Acid number, viscosity and pentane insolubles were determined on the centrifuged oil. Percent total insolubles represents the sum of the oil insolubles and pentane insolubles. Results are shown in Table I.

I claim:

1. A lubricant composition consisting" essentially of arr ester-based fluid of lubricating viscosity, about 0.01 to 5% by weight phenothiazine and about 0.01 to 5% by;

Table 1 Base Fluid Neopentyldiisodecanate Bis(2,2,4-trimethylpentyl) sebacate Lubricant A 1 Additives (Wt. Percent Phenothiazine 0.5 0. 3 0.5 0.2 2 0.2 0 0. 5 2-Aminopyridine 0. 5 0. 2 0. 5 0. 3 0. 5 4-Methy1- aminopyridine. 0. 5 0.3 2,6-Diaminopyridine 0.5 0.3 R1111 N0. 800 l 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Acid No. Rise 23. 6 10. 5 9. 85 5. 94 6. 06 9.19 9. 4 8.16 11.2 8. 90 7. 8 11.0 15. 0 7. 48 2. Percent Vis. Ohange 134. 0 5. 0 21.0 3. 0 64. 0 25.0 11. 5 9. 4 13.0 20. 4 25. 5 l8. 1 85. 4 58.0 20. 2 Percent Oil Inso1ubles .12 2. 5 4.0 4. 5 8.0 2.0 2. 8 2. 5 3.0 3. 8 7. 5 5.0 0.0 trace .6 Percent total Insolubles 2.0 4. 0 9. 0 8.0 10.0 3. 5 5.0 3. 5 5. 0 7. 2 9.0 7. 5 trace 3.0 3 Metal s Corrosion, mg./

-41. 8 16 -34. 8 19. 9 42. 2 .01 -1. 04 09 1. 28 15. 3 2l. 2 2. 83 0.25 2. 33 -0. 8 -.08 -.83 .16 .27 1.47 --.02 .04 0.00 -.06 11 .02 6.94 l.00 .06 02 09 l8 17 32 .09 14 10 14 08 13 06 .02 08 .12

1 n-C -acid-pentaerythritol ester having the following inspection data Acid N0. 0.01, Sap. No. 400, vis. at 210 F., 5.30 cs.; vis. at 100 F., 28.4 cs

Further evidence of the advantages to be obtained by using a composition of this invention are shown in the results of oxygen-adsorption tests at 450 F. The tests were conducted by passing a stream of oxygen at the rate of one cubic foot per hour through 75 grams of the ester fluid containing the inhibitors and comparing the amount of oxygen adsorbed vs. time. The induction period is the time in which little or no oxygen is adsorbed by the fluid. The end of the induction period is signalled by a marked increase in the rate of oxygen adsorption. The results of these tests are shown in Table II.

The induction period serves as a significant measure of the relative efiectiveness of the inhibitors. As shown in Table II, the 2-aminopyridine-phenothiazine synthetic ester-based lubricant composition prevents oxygen uptake by the fluid by more than twice as long as does phenothiazine alone and also more than twice as long as would be expected from the results obtained when using aminopyridine and phenothiazine alone.

4. The lubricant composition of claim 2 containing about 0.1 to 2 percent by weight of phenothiazine.

5. The lubricant composition of claim 4 containing about 0.1 to 2 percent by weight of Z-aminopyridine.

6. The lubricant composition of claim 3 wherein the carboxylic acid of 4 to 12 carbon atoms is selected from the group consisting of aliphatic monocarboxylic acids and aliphatic dicarboxylic acids.

7. The lubricant composition of claim 6 wherein the aliphatic alcohol of 4 to 12 carbon atoms has no hydrogen on a beta carbon atom.

8. The lubricant composition of claim 6 wherein the ratio of aminopyridine to phenothiazine is greater than about 1:1.

9. The lubricant composition of claim 6 wherein the aliphatic alcohol of 4 to 12 carbon atoms has no hydrogen on a beta carbon atom and the ratio of aminopyridine to phenothiazine is greater than about 1:1.

10. The lubricant composition of claim 9 wherein the aminopyridine is Z-aminopyridine.

References Cited in the file of this patent UNITED STATES PATENTS 2,198,961 Dietrich Apr. 30, 1940 2,216,711 Musher Oct. 1, 1940 2,318,196 Chenicek May 4, 1943 2,889,354 Blake et a1. June 2, 1959 OTHER REFERENCES Atkins et al.: Development of Additive and Lubricating Oil Compositions, I. and E. Chem, vol. 39, N0. 4, pp. 491-7, April 1947.

Cohen et al.: Aliphatic Esters, I. and E. Chem, vol. 45, No. 8, pp. 1766-1775, August 1953.

Barnes et al.: Synthetic Ester Lubricants, Lubrication Engineering, pp. 454-458, August 1957. 

1. A LUBRICANT COMPOSITION CONSISTING ESSENTIALLY OF AN ESTER-BASED FLUID OF LUBRICATING VISCOSITY, ABOUT 0.01 TO 5% BY WEIGHT PHENOTHIAZINE AND ABOUT 0.01 TO 5% BY WEIGHT AMINOPYRIDINE AND EFFECTIVE TO RETARD OXIDATION OF SAID ESTER-BASED FLUID AT TEMPERATURES IN EXCESS OF 400*F., SAID ESTER-BASED FLUID BEING OF AN ESTER OF AN ALCOHOL OF 4 TO 12 CARBON ATOMS AND A CARBOXYLIC ACID OF 4 TO 12 CARBON ATOMS. 